The present invention relates to an air suspension system with an air drier for adjusting a vehicle height by supplying air to and discharging air from an air actuator provided for each wheel of the vehicle.
There are currently many air suspension systems for adjusting a vehicle height by supplying the compressed air to and discharging it from the air actuators. The compressed air is usually dried to prevent condensation in the air suspension system. The air drier, however, has limited capacity, thus its capacity for absorbing moisture will be lost eventually. To eliminate this problem, some prior-art systems have been proposed. One example is the air suspension system in Japanese Published Unexamined Utility Model Application S58-104711. When the pressure in an accumulator is low, the air that is discharged from an air actuator (air spring) to lower the vehicle height is compressed and then stored in the accumulator. This reduces the load on the compressor and the amount of pumping energy required. When the pressure in the accumulator is high, the air discharged from the air actuator to lower the vehicle height is released into the atmosphere through the air drier. This restores the drier's dehumidifying capacity. In another conventional air suspension system in Japanese published unexamined patent application S61-99730, the air discharged from the air actuator to lower the vehicle height is released into the atmosphere through the air drier to restore the drier's moisture-absorbing capacity. In addition, in this air suspension system, when the pressure in the accumulator is higher than a predetermined value, the compressed dry air in the accumulator is released into the atmosphere through the drier until the pressure in the accumulator reaches a preset value. Thus, the dehumidifying capacity of the drier is efficiently restored.
These prior-art systems, however, still have some deficiencies. In the first example, air from the actuator must pass through an air throttle valve before discharge into the atmosphere. The valve reduces the air pressure in the drier, which improves the restoration rate of the desiccant in the drier but also increases the time needed to lower the vehicle height. This has the drawback that it takes longer to lower the vehicle height.
In the second example, restoration of the desiccant is more efficient but again a throttle valve is used so vehicle height lowering time remains excessive. Moreover, since the air discharged when lowering the vehicle height is not recycled, the load on the compressor is large.